Components salvage session - comments

Discussion in 'Off-Topic' started by atferrari, Mar 28, 2014.

  1. atferrari

    Thread Starter AAC Fanatic!

    Jan 6, 2004
    2,648
    764
    I am posting here because you will learn nothing; only comments / rant follow.

    This mornig I run a heat gun brute-force salvage session on several extincted motherboards and some PCI cards. I was interested only in the connectors and the crystals. Just that. I accepted beforehand that whatever else would be lost.

    No matter how you do it, whit a heat gun, the ICs and components get literally cooked even if the board is kept upside down for them to fall freely on a tray. They were even hot to touch. I read many comments saying that this way you can end with a bare board. While it is true it is not even worth the effort to have a collection of components cooked beyond hope.

    The first to fall, from the group being heated up, were the tantalum caps and crystals. Some connectors, long ones, could take some time and a not so gentle tap on the board helped sometimes. When tapping the board, if any terminal got bent; the connector risked to stay there, hanging forever. More tapping.

    Hot air from a smd rework station did not help at all. Evidently, air volume is too low to be of any use when applied to the solder side of the connectors.

    On the contrary, gently heating the whole board with a more friendly heat gun, and then using a common desoldering technique, ICs and discretes come out in fairly well condition. I used this technique in the past with excellent results and just once today.

    Motherboards found to differ a lot from each other. From one of them I got 5 crystals (one, the typical 32,768).

    In many of them, the LM386 (SMD) was present.

    And old one, still with 74LS logic and the AMI BIOS in two chips (ODD and EVEN)

    Another motherboard, had NO crystal at all. How comes?

    And the last: encouraged by the previous experiences, I was brave enough to recognize the deat of my PC. (It took me time. It happened some 20 years ago and it was my first one, where I learnt that BASIC was not available as in my Timex Sinclair.

    I finally stripped the board and found an incredible (to me) 48-MHz crystal. The highest ever I could see in a MB.

    Underlying connections between things do exist and it is up to you to notice them: the crystaless PC above and this one were of the same brand: WARRANTY VOID IF REMOVED.
     
    Last edited: Mar 28, 2014
    #12 likes this.
  2. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    It's very hard to remove components from a multi-layer motherboard. The inner layers suck away all the heat.
    :)
     
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,067
    3,837
    I hold the component with a pair of needle nose pliers with the weight of the board. A quick hit with the hit air pops most. Like cooking rare meat, a hot hot heat gun is best (so you can seer the outside before the inside starts cooking). Melting the solder before the component overheats.

    Also, work different parts of the board - pick the next component on a different quadrant to prevent one part of the board from getting too hot.
     
  4. #12

    Expert

    Nov 30, 2010
    16,343
    6,828
    Hanging a forceps on the part works fairly well and leaves you with an extra hand free.
     
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